Energetics and electronic structures of carbon nanotubes with adatom–vacancy defects

We report first-principle total-energy electronic-structure calculations in the density functional theory performed for carbon nanotubes with a defect consisting of a pair of an adatom and a vacancy. We find that the activation barriers for formation and healing of the defect are ∼10 and 2 eV, respectively, indicating the possibility of defect healing under moderate conditions. The defect is found to induce two gap states with characteristics that strongly depend on its arrangement. Further, the metal–insulator transition takes place on the (9, 0) nanotube owing to the formation of gap states.